Hydroformylation reactions substituted olefins

Example 8.3. Phosphine-substituted cobalt hydrocarbonyls as hydroformylation catalysts. Extensively studied catalyst systems with complex equilibria include phosphine-substituted hydrocarbonyls of cobalt, HCo(CO)3Ph, where Ph stands for a tertiary organic phosphine. They are modifications of the original oxo catalyst, HCo(CO)4. Like the latter, they catalyze the oxo or hydroformylation reaction of olefins to aldehydes one carbon number higher ... 

The hydroformylation reaction is carried out in the Hquid phase using a metal carbonyl catalyst such as HCo(CO)4 (36), HCo(CO)2[P( -C4H2)] (37), or HRh(CO)2[P(CgH3)2]2 (38,39). The phosphine-substituted rhodium compound is the catalyst of choice for new commercial plants that can operate at 353—383 K and 0.7—2 MPa (7—20 atm) (39). The differences among the catalysts are found in their intrinsic activity, their selectivity to straight-chain product, their abiHty to isomerize the olefin feedstock and hydrogenate the product aldehyde to alcohol, and the ease with which they are separated from the reaction medium (36). 

Betzemeier et al. (1998) have used f-BuOOH, in the presence of a Pd(II) catalyst bearing perfluorinated ligands using a biphasic system of benzene and bromo perfluoro octane to convert a variety of olefins, such as styrene, p-substituted styrenes, vinyl naphthalene, 1-decene etc. to the corresponding ketone via a Wacker type process. Xia and Fell (1997) have used the Li salt of triphenylphosphine monosulphonic acid, which can be solubilized with methanol. A hydroformylation reaction is conducted and catalyst recovery is facilitated by removal of methanol when filtration or extraction with water can be practised. The aqueous solution can be evaporated and the solid salt can be dissolved in methanol and recycled. 

Interception of the reaction sequence at the alkylcobalt carbonyl stage before carbonyl insertion, and hydrogenation of this intermediate, produces an alkane. This undesired side reaction is only minor (1-3%) in cobalt-catalyzed hydroformylation of a nonfunctional olefin, but may become predominant with phenyl- or acyl-substituted olefins. Ethylbenzene has been obtained in >50% yield from styrene (37), and even more alkane was obtained from a-methylstyrene (35). 

The aqueous biphasic processes require a minimum solubility of the reactants S in the catalyst phase [196, 205]. Therefore, hydroformylation of higher olefins (approx. > Cg) or functionally substituted olefins is more difficult but offers various advantages, such as the simplification of reaction sequences and reduced expenditure for the catalyst cycle. So far, work on these biphasic processes for the conversion of higher olefins, except for Kuraray s recent devel-... 

The enantioselective hydroformylation process confronts a series of challenges. First, the hydroformylation of alkenes tends to form linear over branched products. Thus, enantioselective hydroformylation of alkenes must be conducted with uns)rmmetrical "vinylidenic" olefins (2,2-disubstituted) that establish a stereocenter at the carbon p to the carbonyl group, or with mono-substituted olefins that form the branched product. As noted above, vinylarenes, vinyl acetates, and other olefins bearing electron-withdrawing groups, form branched products. Thus, reactions of these olefins have been the greatest focus of enantioselective hydroformylations. 

Both platinum and rhodium catalysts have been studied for enantioselective hydroformylation. The asymmetric hydroformylation of an itaconate derivative occurs with the highest selectivity in the presence of platinum catalysts (Equation 17.17). However, the chemical yields of branched aldehydes from reactions catalyzed by platinum catalysts are typically low. Therefore, enantioselective hydroformylation of mono-substituted olefins with platinum catalysts have generally been unsatisfactory, and most effort has been spent on developing rhodium catalysts for asymmetric hydroformylation. 

Thus, [HRh(C0)(TPPTS)3]/H20/silica (TPPTS = sodium salt of tri(m-sulfophenyl)phopshine) catalyzes the hydroformylation of heavy and functionalized olefins,118-122 the selective hydrogenation of a,/3-unsaturated aldehydes,84 and the asymmetric hydrogenation of 2-(6 -methoxy-2 -naphthyl)acrylic add (a precursor of naproxen).123,124 More recently, this methodology was tested for the palladium-catalyzed Trost Tsuji (allylic substitution) and Heck (olefin arylation) reactions.125-127... 

Because the thermal separation of products has been substituted by a liquid-liquid separation, the two phase technology should be best suited for hydroformylation of longer chain olefins. But with rising chain length of the olefins the solubility in the aqueous catalyst phase drops dramatically and as a consequence the reaction rate. Only the hydroformylation of 1-butene proceeds with bearable space-time yield. This is applied on a small scale for production of valeraldehyde starting from raffinate II. Because the sulfonated triphenylphosphane/rhodium catalyst exhibits only slow isomerization and virtually no hydroformylation of internal double bonds, only 1-butene is converted. The remaining raffinate III, with some unconverted 1-butene and the unconverted 2-butene, is used in a subsequent hydroformy-lation/hydrogenation for production of technical amylalcohol, a mixture of linear and branched C5-alcohols. 

Abstract Aldehydes obtained from olefins under hydroformylation conditions can be converted to more complex reaction products in one-pot reaction sequences. These involve heterofunctionalization of aldehydes to form acetals, aminals, imines and enamines, including reduction products of the latter in an overall hydroaminomethylation. Furthermore, numerous conversions of oxo aldehydes with additional C.C-bond formation are conceivable such as aldol reactions, allylations, carbonyl olefinations, ene reactions and electrophilic aromatic substitutions, including Fischer indole syntheses. 

Veiy recently it was disclosed, that the water-soluble dinuclear complex obtained in the reaction of [ RhCl(COD) 2] and 11-mercaptoundecanoic acid catalyzed the aqueous/organic biphasic hydroformylation of styrene and various arene-substituted styrenes with good activity and useful selectivity to the branched aldehydes (Scheme 4.6) [82], Below pH 4 the acid form of the complex [ Rh(p-S(CH2)ioC02H)(COD) 2] precipitated virtually quantitatively but could be redissolved in water on addition of base. Importantly, higher olefins could also be hydroformylated by this catalyst (for 1-octene TOP = 17.5 h at 55 °C, 35 bar syngas, n/i = 1.0). 

Example 6.5. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [30], The pathway 6.9 of olefin hydroformylation with the "oxo" catalyst, HCo(CO)4, has been shown in Example 6.2 in Section 6.3. For phosphine-substituted catalysts, HCo(CO)3Ph (Ph = organic phosphine), the pathway olefin — aldehyde is essentially the same. However, these catalysts also promote hydrogenation of aldehyde to alcohol (Examples 7.3 and 7.4) and of olefin to paraffin (Example 7.5). Moreover, straight-chain primary aldehydes under the conditions of the reaction undergo to some extent condensation to aldol, which is subsequently dehydrated and hydrogenated to yield an alcohol of twice the carbon number (e.g., 2-ethyl hexanol from n-butanal see Section 11.2). The entire reaction system is... 

Example 7.6. Olefin hydroformylation with phosphine-substituted cobalt hydrocarbonyl catalyst [7], The overall reaction system of olefin hydroformylation with a phosphine-substituted cobalt hydrocarbonyl catalyst to produce alcohol, paraffin, and a heavy alcohol has been shown in Example 6.5 (Section 6.5) ... 

The example of the mass-transfer effect in olefin hydroformylation is interesting in still another respect. If a phosphine-substituted cobalt hydrocarbonyl is used as catalyst in combination with 1-olefin as reactant, a very strong burst of reaction ensues at the reactor inlet or at start of a batch reaction (see Example 12.1). 

Neutral catalysts or catalyst precursors based on fluorinated ligand systems have been applied in compressed CO2 to a broad range of transformations such as Zn- and Cr-catalyzed copolymerization of epoxides and CO2 [53, 54], Mo-catalyzed olefin metathesis [9], Pd-catalyzed coupling reactions [43, 55, 56] and Pd-catalyzed hydrogen peroxide synthesis [57]. Rhodium complexes with perfluoroalkyl-substituted P ligands proved successful in hydroformylation of terminal alkenes [28, 42, 44, 58], enantioselective hydroformylation [18, 59, 60], hydrogenation [61], hydroboration [62], and polymerization of phenylacetylene... 

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